Rewrite the following expression by factoring it completely:
15a³b⁴ + 20a²b² + 40ab³

• A. 5ab²(3a²b² + 4a + 8b)
• B. 2ab²(3a²b² + 4a + 20b)
• C. 5a²b²(3ab² + 4a + 8b)
• D. 2a​²b²(3ab² + 4a + 20b)

Answer: (A)